The invention concerns a purifier for gaseous fluids, and more particularly a turbine having a rotor and including means for adsorbing impurities from the gaseous fluid.
By turbine is meant any apparatus whose rotor turning at high speed produces a centrifugation. In this description, the word turbine is synonymous with centrifugal ventilator.
Conventional air cleaning or purifying apparatus include screens of filter paper or fabric, or baskets (corfs) or baffles enclosing active substances in granular or liquid form and through which air is drawn or blown. Active carbon, beds of granular potassium permanganate and sawdust impregnated with manganese dioxide have all been proposed as active filtering material which retains impurities in the air by physical or chemical action. These known cleaning apparatus require means for strongly pulsing the air which are sufficiently powerful to overcome the head loss produced during passage of the air through the filters. The consumption of power and of costly chemical products used is high and is contrary to the efforts being made to economize power and depletable materials. Also, the noise produced by the pulsed air is a nuisance and cleaning and replacement of the filters is generally a difficult and dirty operation.
The gaseous-fluid cleaning apparatus according to the invention is characterized in that the filter is comprised of an adsorbent material able to retain particles in suspension in the gaseous fluid and disposed in such a manner that the flux of gaseous fluid produced by the turbine licks its surfaces without passing through them. The turbine is arranged to produce a flux of fluid with turbulent flow.
In preferred embodiments, the rotor of the turbine is comprised of said adsorbent material and hence provides both a ventilating function and a cleaning function.
According to the nature of the cleaning or purification to be carried out, the manner of construction of the turbine can vary.
In one preferred embodiment, the turbine comprises at least two disks having a common axis of symmetry or of rotation and which are spaced apart from each other. At least one of the disks is of conical shape. The distance between the two disks at the peripheries of the purifier is smaller than the distance between them at their centers. A central suction opening of circular shape is provided in at least one of the two disks.
The foregoing behaves not only as a radial or centrifugal fan but also as a filter which purifies the gaseous liquid which it displaces.
The purifying ability of the purifier having the shape of a filtering rotor which is the subject of the present invention is not caused by the same things as with conventional filters, which retain contaminants by absorption. The filtering rotor of the present invention acts by adsorption, i.e. it retains on its surface molecules of a gas or of a solution (aerosols) or solid particles (dust, bacteria, etc.) suspended in the gaseous fluid which is displaced upon the rotation of the filtering rotor. A true absorbent acts by physical, physical-chemical, or chemical means.
Scientific encyclopedias state that adsorption occurs with pulverulent or porous solids that have the property of retaining on their surfaces the molecules in gaseous or liquid phases that come in contact with them. This physico-chemical surface phenomenon is distinguished from the phenomenon of absorption, which is not a surface phenomenon. The solid is called the adsorbent and the gas or liquid the adsorbate. The adsorbents may be solid or liquid and the adsorbates may be gaseous, liquid, in solution or even in suspension. It does not appear that up to now any great amount of attention has been paid to the adsorption phenomena of a solid on a solid or of a liquid on a solid. The filtering rotor of the present invention also satisfies these two functions.
In the boundary layer theory of fluid mechanics, one studies the special features of the movement of a viscous liquid in the case of high Reynolds numbers. Within the boundary layer, which is the layer of fluid in contact with a moving solid (or vice versa), a region of laminar or turbulent flow may exist. The passage from laminar flow to turbulent flow in the boundary layer takes place when the Reynolds number reaches its critical value.
The present invention utilizes the consequences of the system of turbulent flow in which the fluid particles follow disorganized paths which are caused by forces of the rubbing of the fluid against moving solid walls. In turbulent flow, the value of the velocity of the particles of the fluid at each point in space undergoes continuous variations, both in value and in direction. This random movement of the masses of the fluid favors excellent contact between the fluid and the solid surfaces forming the filtering rotor. The capture of the solid or liquid particles suspended in the fluid upon contact with the solid surfaces which surround them is better when the roughness of these surfaces is greater.
It has not been possible until now to establish theoretically the exact form of the law of resistance governing the turbulent boundary layer. Thus, for this purpose, the results of experimental research on the boundary layer are used in addition to various simplifying hypotheses. For this reason, modern methods of calculating the turbulent boundary layer are semi-empirical and their precision depends upon the authenticity of the test materials taken as basis for the determination of the laws of the distribution of velocity and resistance. With a few exceptions, all the research work has been carried out in order to avoid the appearance of turbulent movements in contact with solids moving in a gaseous fluid (or vice versa), while the object of the present invention is to create such turbulent movements in order to derive therefrom an effect which has not been utilized up to now, namely the filtration of gaseous fluids by physical or chemical adsorption, or both simultaneously, when the constituent material of the filtering rotor i.e., the adsorbent, is impregnated with a chemical reagent whose catalytic effect chemically transforms the contaminating gas suspended in the fluid which is to be purified. This chemical adsorption phenomenon is also known as "chemisorption".
Rotation of the filtering rotor causes the aspiration of the contaminated gaseous fluid, assures its purification by adsorption, and discharges a purified fluid. The rotor may turn in the open air in the manner of a simple axial fan. This causes a movement of convection of the ambient air and thereby provides a closed-circuit ventilation of the room in which it is located, and it progressively purifies the air in the room. The filtering rotor may alternatively be enclosed in a housing. Then polluted air is removed from one enclosure via a conduit and is discharged in purified condition into another enclosure.
Measurements carried out on a chromic-acid aerosol have made it possible to note average filtration efficiencies of between 92.8% and 98.5% after a single passage of the polluted air through the housing with different constructions of the filtering rotor according to the invention.
The constituent material of the filtering rotor is preferably a roughened surface material or a rugous surface material. The roughness may be so coarse as to produce visible depressions in the surfaces. It may be comprised of rigid or flexible, woven or agglomerated, fibrous material. Examples of such materials are cardboard-like material, corrugated paper, sheets of porous or alveolar plastics material, or any other stuck non-woven fibers (cotton, polyester, glass, etc.), or woven fibers. Furthermore, the material can be impregnated or coated with at least one chemical reagent that is capable of reacting with contaminating gases (chemisorption) or with odiferous particles contained in the gaseous fluid to be purified and which it is desired to remove. Such a chemical reagent will be chosen so that when the polluting gases or smelly particles come into contact with the impregnated or coated surfaces, it transforms them into salts which remain fixed on the rugous surfaces.
The absorbent material may also be impregnated with a bacteriological agent, for example germicide solutions for killing micro-organisms contained in the fluid to be cleaned.
In a preferred embodiment of the invention, the chemical reagent is an oxidizing agent, in particular a permanganate and/or activated manganese dioxide. Activated MnO.sub.2 is well known in the art; it exerts a greater and more rapid oxidizing action than ordinary MnO.sub.2, and is usually formed by a careful partial reduction of KMnO.sub.4. It is believed that the activated MnO.sub.2 still contains some KMnO.sub.4. It has been found that, most surprisingly, activated MnO.sub.2 is formed quasi-automatically by impregnating paper with an aqueous solution of KMnO.sub.4. Preferably, as material of disks of the rotor, one uses cellulose which is as pure as possible. It is thought that the cellulose acts as a reducing agent for transforming KMnO.sub.4 into activated MNO.sub.2.
The KMnO.sub.4 /MnO.sub.2 system has another advantage. Since the salts of bivalent manganese (Mn(II)) which are formed when the oxidizing agent is depleted are white, this forms an indicator for the system. The decoloration thus indicates that the active material is reaching exhaustion, and the filter is changed.
Other oxidizing agents may be used for the impregnation or coating of the rotors: for example salts, oxides or hydroxides of Fe(III), the chromates or bichromates of salts of Sn(IV), Pb(IV), Ce(III), Ti(IV), vanadium, etc. It is also possible to use cyanoferrates (III) and in addition composities of H.sub.2 O.sub.2, for example perborates, urea peroxide etc. These oxidizing agents, including KMnO.sub.4 and activated MnO.sub.2, may be used alone or mixed.
Use of an oxidizing agent is preferred since the most usual impurities of air are easily oxidizable. These impurities are, for example, H.sub.2 S, SO.sub.2, solvent vapors (alcohols, ketones, esters, hydrocarbons, aldehydes), amines, greases, mercaptans, and so on.
Some of these impurities when oxidized give acidic products. For example, H.sub.2 S and SO.sub.2 are oxidized to SO.sub.3. Normally, these oxidized products are retained by the material of the sheets, for example according to the following relationship: EQU SO.sub.3 +MnO.fwdarw.MnSO.sub.4,
the MnO being the product of the reaction. EQU SO.sub.2 +MnO.sub.2 .fwdarw.SO.sub.3 +MnO.
To further increase the retaining power of the filter, one may add to the oxidizing agent with which the rotor disks are impregnated or coated, a base such as KOH, NaOh, Na.sub.2 CO.sub.3 or K.sub.2 CO.sub.3. It is also possible to apply the oxidizing agent to the median part of the rotor and to impregnate or coat the periphery with the base. As a variation, a cylindrical (or non-cylindrical) sheet is placed about the rotor and the air leaving the rotor comes to hit this sheet which is impregnated with a different reagent to that of the rotor; if it is for example impregnated with a base, this sheet will thus retain the acidic products of oxidation.
The material can be impregnated or coated with fragrance-imparting particles or perfumes which it is desired to introduce into the purified fluid.
The material may be treated with a fire-retarding agent in order to prevent a fire from developing due to a too violent reaction with the impurities or due to the gaseous fluid reaching a critical temperature.
An object of the invention is to provide an apparatus for cleaning gaseous fluids which is of simple structure, economical, easy to service, quiet in operation, has a low power consumption and which is capable of cleaning fluids by adsorption of impurities.